Network refactor

network.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+set -eu
+
+[ ! -e /dev/net/tun ] && echo "Error: TUN interface not available..." && exit 85
+
+# A bridge of this name will be created to host the TAP interface created for
+# the VM
+QEMU_BRIDGE='qemubr0'
+
+# DHCPD must have an IP address to run, but that address doesn't have to
+# be valid. This is the dummy address dhcpd is configured to use.
+DUMMY_DHCPD_IP='10.0.0.1'
+
+# These scripts configure/deconfigure the VM interface on the bridge.
+QEMU_IFUP='/run/qemu-ifup'
+QEMU_IFDOWN='/run/qemu-ifdown'
+
+# The name of the dhcpd config file we make
+DHCPD_CONF_FILE='dhcpd.conf'
+
+function default_intf() {
+    ip -json route show |
+        jq -r '.[] | select(.dst == "default") | .dev'
+}
+
+# First step, we run the things that need to happen before we start mucking
+# with the interfaces. We start by generating the DHCPD config file based
+# on our current address/routes. We "steal" the container's IP, and lease
+# it to the VM once it starts up.
+/run/generate-dhcpd-conf $QEMU_BRIDGE > $DHCPD_CONF_FILE
+default_dev=$(default_intf)
+
+# Now we start modifying the networking configuration. First we clear out
+# the IP address of the default device (will also have the side-effect of
+# removing the default route)
+ip addr flush dev "$default_dev"
+
+# Next, we create our bridge, and add our container interface to it.
+ip link add "$QEMU_BRIDGE" type bridge
+ip link set dev "$default_dev" master "$QEMU_BRIDGE"
+
+# Then, we toggle the interface and the bridge to make sure everything is up
+# and running.
+ip link set dev "$default_dev" up
+ip link set dev "$QEMU_BRIDGE" up
+
+# Prevent error about missing file
+touch /var/lib/misc/udhcpd.leases
+
+# Finally, start our DHCPD server
+udhcpd -I $DUMMY_DHCPD_IP -f $DHCPD_CONF_FILE 2>&1 &
+
+exit 0